Currently under development is AHS (Automated Highway System) for automated driving control. It is a system in which various kinds of information are exchanged between an infrastructure installed in roads and vehicles, thereby continuously providing data and adding thereto vehicle control information, in order to achieve automated driving. Currently used as the infrastructure for providing the vehicle control information are magnetic nails, which are embedded in the road surface and whose positions are successively detected by a vehicle, whereby the position and orientation of the vehicle is recognized.
In order to enhance the stability and reliability in the automated vehicle in the AHS, it is necessary to detect the magnetic nails more securely. This may be achieved by a technique in which the magnetic force of each of the magnetic nails embedded in a cruising lane with predetermined intervals is enhanced so that the magnetic sensor can detect it more securely, and a technique in which the magnetic sensor attached to the lower face of the vehicle body is positioned as close to the magnetic nails as possible so that the magnetic flux density increases to allow the current generated by electromagnetic induction to be detected more securely.
Since a magnetic nail is made of a permanent magnet, from the viewpoint of its size and cost, it is physically and structurally too restricted to increase the magnetic force generated thereby. Thus preferred as the technique for detecting the magnetism of magnetic nails is a method in which the magnetic sensor is positioned as close to the magnetic nails embedded in the road surface as possible. Since it has empirically been known that the magnetic force of the conventional magnetic nail cannot be distinguished from geomagnetism when the magnetic sensor is separated from the magnetic nail surface on the road by about 15 cm or more, it is necessary for the magnetic sensor to be positioned with a shorter distance to the magnetic nail surface.
Also, when a vehicle is running, due to damping thereof, the distance from the road surface to the magnetic sensor may vary, whereby the magnetic sensor may fail to detect magnetic nails. Accordingly, it is desirable that the magnetic sensor be positioned as close to the road surface as possible in order to achieve more secure detection. Nevertheless, when the magnetic sensor is positioned close to the road surface of a cruising lane in order to detect magnetism more securely, the road clearance of the vehicle may greatly fluctuate due to the damping and pitching of the vehicle, irregularities of the road surface, or the like, whereby the magnetic nails may not be detected stably.